Microelectromechanical systems (i.e., “MEMS”) are highly miniaturized devices that can be configured to perform a wide variety of functions. For example, a MEMS device can be implemented as an accelerometer to measure the acceleration of a moving body. One type of MEMS accelerometer, for example, has a suspended mass that, in response to an acceleration, moves relative to an underlying substrate. Acceleration thus may be calculated as a function of the movement of the suspended mass relative to its underlying substrate.
Because of their relatively small size, the mechanical structures of MEMS devices (e.g., the suspended mass in the above noted accelerometer) typically are both fragile and sensitive. Accordingly, many seemingly innocuous things can adversely impact MEMS performance, such as dust, moisture, and static electricity. The art has responded to this problem by isolating sensitive MEMS mechanical structures from the outside environment. For example, one isolation method bonds a cap over the mechanical components.
Although generally satisfactory for isolating MEMS structure, this solution creates other problems. In particular, the cap can accumulate a relatively large static electric charge that can adversely affect device performance and/or damage the MEMS device.